Wafer Surface Conditioning for Stability in Fab Environment

ABSTRACT

Hydroxyl moieties are formed on a surface over a semiconductor substrate. The surfaces are silylized to replace the hydroxyl groups with silyl ether groups, the silyl ether groups being of the form: —OSiR 1 R 2 R 3 , where R 1 , R 2 , and R 3  are each hydrocarbyl groups comprising at least one carbon atom. Silylation protects the wafers from forming defects through hydrolysis while the wafers are being transported or stored under ambient conditions.

FIELD

The present disclosure relates to systems and methods for integrated circuit device manufacturing.

BACKGROUND

With hundreds of process steps and expensive equipment, queue time control is critical to the economic viability of an integrated circuit device manufacturing facility. As wafers are processed through the facility, they must often be protected from the ambient environment. If, following completion of processing in one tool, the next tool is not immediately available, wafers must often be stored in a protected environment. The wafers can be stored within the tool in which they have completed processing, but this forces the tool to become idle. Alternatively, the wafers can be stored in an environmentally controlled storage rack. Such storage racks are additional structures that take up valuable plant floor space and require additional capital investment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a hydrolysis reaction.

FIG. 2 illustrates cross-linking of hydroxyl moieties on a wafer surface.

FIG. 3 provides a flow chart of a process according to one embodiment of the present disclosure.

FIG. 4 illustrates a silylation reaction according to an embodiment of the present disclosure.

FIGS. 5-8 provide flow charts of processes according to an additional embodiment of the present disclosure.

FIGS. 9-13 illustrate a wafer undergoing a lithography process.

DETAILED DESCRIPTION

The inventors have determined that wafers exposed to ambient conditions within an integrated circuit manufacturing facility can develop defects through moisture-induced hydrolysis and subsequent cross-linking. FIG. 1 illustrates moisture-induced hydrolysis of an ether group attached to a Si atom on a surface 10 of a wafer. The hydroxyl moieties are reactive and can cross-link as illustrated by FIG. 2. Cross-linking can occur over extended areas, changing the surface topography and producing defects. The inventors have further determined that silylation can protect the wafers sufficiently to allow them to be exposed to these ambient conditions.

The term “silylation” as used herein is the substitution of a hydrogen atom bound to a an oxygen atom (—OH) by a silyl group to form a silyl ether. A silyl ether has the form: —OSiR¹R²R³, where R¹, R², and R³ can be any suitable ligands. In some embodiment, R¹, R², and R³ are all the same and the silyl ether is of the form: —OSiR¹ ₃. In some embodiments, R¹, R², and R³ are hydrocarbyl groups, which are generally effective for protecting wafer surfaces. Examples of hydrocarbyl groups include alkyl, vinyl, aryl, allyl, and alkynyl groups.

Silyl ethers are resistant to both basic and acid hydrolysis. This can be due in part to the hydrophobicity of the silyl group and in part to steric hindrance. Steric hinderance can be enhanced by providing bulkier R¹, R², and R³, e.g., trialkylsilyl. Accordingly, in some embodiments, R¹, R², and R³ are hydrocarbyl groups each having two or more carbon atoms. Electron-withdrawing R¹, R², and R³ groups, e.g., phenyl groups, can be selected to increase stability to acidic hydrolysis while decreasing stability to basic hydrolysis and vice versa. Depending on anticipated conditions, in some embodiments R¹, R², and R³ are substantially more electron withdrawing than —CH₃ and in some other embodiments R¹, R², and R³ are substantially less electron withdrawing than —CH₃.

FIG. 3 illustrates an example process 100 according to an embodiment provided by the present disclosure. The process 100 begins with hydrolysis 101 of an exposed surface 10 as illustrated in FIG. 1. A surface may be all or partially hydrolyzed incidentally to its formation or as a consequence of processing for another purpose. Hydrolysis can be accomplished in any suitable manner. Hydrolysis can include the application of purified water such as deionized or distilled water. Hydrolysis can be facilitated by an acid or a base. In some embodiments, hydrolysis comprises treating the exposed surface 10 with an acidic solution. Dilute hydrofluoric acid (DHA) and Buffer Oxide Etch (BOE) can be particularly effective. Accordingly, in some embodiments hydrolysis comprises treating the exposed surface 10 with a solution comprising hydrofluoric acid.

Process 100 of FIG. 3 continues with silylation 103. Silylation involves treating the surface 10 with a silyliating agent. A silyliating agent is generally of the form: Y—(OSiR¹R²R³)_(N), where N is an integer between 1 and the valence of Y. Y can be any suitable species. Examples of species that can be suitable for Y include F, Cl, Br, I, amines, and amides. Where R¹, R², and R³ are all methyl groups, the silyliating agent can be any of allyltrimethylsilane, N,O-Bis(trimethylsilyl)acetamide (BSA), N,O-Bis(trimethylsilyl)carbamate (BSC), N,N-Bis(trimethylsilyl)formamide (BSF), N,N-Bis(trimethylsilyl)methylamine, Bis(trimethylsilyl) sulfate (BSS), N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA), N,N′-Bis(trimethylsilyl)urea (BSU), (Ethylthio)trimethylsilane, Ethyl trimethylsilylacetate (ETSA), Hexamethyldisilane, Hexamethyldisilazane, Hexamethyldisiloxane (HMDSO), Hexamethyldisilthiane, (Isopropenyloxy)trimethylsilane (IPOTMS), 1-Methoxy-2-methyl-1-trimethylsiloxypropene, (Methylthio)trimethylsilane, Methyl 3-trimethylsiloxy-2-butenoate, N-Methyl-N-trimethylsilylacetamide (MSA), Methyl trimethylsilylacetate, N-Methyl-N-trimethylsilylheptafluorobutyramide (MSHFBA), N-Methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), (Phenylthio)trimethylsilane, Trimethylbromosilane (TMBS), Trimethylchlorosilane (TMCS), Trimethyliodosilane, (TMIS), 4-Trimethylsiloxy-3-penten-2-one (TMSacac), N-(Trimethylsilyl)acetamide, (TMS-acetamide), Trimethylsilyl acetate, Trimethylsilyl azide, Trimethylsilyl benzenesulfonate, Trimethylsilyl cyanide (TMSCN), N-(Trimethylsilyl)diethylamine (TMSDEA), N-(Trimethylsilyl)dimethylamine (TMSDMA), Trimethylsilyl N,N-dimethylcarbamate (DMCTMS), 1-(Trimethylsilyl)imidazole (TMSIM), Trimethylsilyl methanesulfonate, 4-(Trimethylsilyl)morpholine, 3-Trimethylsilyl-2-oxazolidinone (TMSO), Trimethylsilyl perfluoro-1-butanesulfonate (TMS nonaflate), Trimethylsilyl trichloroacetate, Trimethylsilyl trifluoroacetate, and Trimethylsilyl trifluoromethanesulfonate (TMS triflate). Chemically analogous silyliating agents can be identified by substituting one or more of the methyl groups with other desired R¹, R², and R³ in the foregoing examples. FIG. 4 illustrates the reaction where the silyliating agent is HMDS. A mixture silyliating agents can also be used.

The process 100 continues with an optional action of transporting 105, which is transporting the silylized wafer through the ambient environment of a manufacturing facility. Processing of wafers typically takes place in a series of modules, tools, or tracks each having a controlled environment. For example, separate modules may be provided for CVD coating, cleaning, lithographic patterning, and etching. Between modules, tools, or tracks, it may be convenient to move wafers through or store wafers in the ambient environment. The process 100 illustrates this with an optional action of transporting 105 and the subsequent action 107, which is further processing in a separate module, tool, or track from the one in which silylation takes place.

While silylation according to the present disclosure can be used to protect a wafer from exposure to the ambient environment, the silylation can also be used for other purposes. In some embodiments, silylation is used to protect a wafer from polar contaminants, which protection may be desired within the same process unit (module, tool, or track) within which silylation takes place. In some other embodiments, silylation renders the surface hydrophobic, which facilitate uniform wetting by non-polar liquids and uniform coating using a liquid precursor carried in a non-polar solution.

FIG. 5 provide a flow chart for a process 200A, which is an example of embodiments in which silylation is useful within the same process unit in which silylation takes place. In process 200A, silylation takes place and is functional within a lithography module 210. FIGS. 9-13 illustrate a wafer 400 being processed through the module 210. Action 201 forms a functional coating 401 over a surface 402 of the wafer 400. A functional coating can be any coating that is patterned and subsequently becomes part of an integrated circuit device. A functional coating can be a dielectric coating, a polysilicon coating, or another type of conductive coating. A functional coating can include multiple layers having various compositions.

In process 200A of FIG. 5, silylation 103 follows action 201, forming functional coating 401. Hydrolysis 101 can be applied after forming the functional coating 401 and before silylation if necessary. In process 200A, silylation 103 modifies a surface 404 of the functional coating 401. Silylation 103 protects the surface 404 during subsequent processing, such as curing 203. Curing 203 can include heating then cooling the wafer 400. Silylation protects the wafer surface 404 formed by the functional coating 401 against hydrolysis and from contamination by polar contaminants during curing 203.

Processing within the lithography module 210 can further include action 205, which forms a photoresist coating 403 as shown in FIG. 11, action 207, which is selectively exposing the photoresist 207 according to a pattern defined by a photolithography mask, and action 209, which is developing the photoresist 403 to pattern it as shown in FIG. 12. In some embodiments a precursor for the photoresist 403 is applied with a non-polar solvent and silylation 103 facilitate coating surface 404 with photoresist 403. In some embodiments, silylation 103 protects the surface 404 from hydrolysis and or contamination by polar contaminants during developing 209. The process 200A proceeds with etching 211, which takes place in the etch module 220. Etching 211 is an etch of the functional coating 401 in the pattern of the mask 403 as shown in FIG. 13.

FIG. 6 provide a flow chart for a process 200B, which is another example of embodiments in which silylation 103 is useful within the same process unit in which silylation 103 takes place. Process 200B is similar to process 200A except that silylation 103 takes place prior to forming the functional coating 401 and protects the wafer surface 402. In this example, silylation 103 primes the surface 402 to receive a precursor for the functional coating 401.

In some embodiments, hydrolysis and silylation take place immediately after formation of the surface protected by silylation. In these embodiment, silylation generally takes place within the same process unit as the one in which the protected surface is formed. In some other embodiments, silylation takes place in a separate module following a cleaning of the protected surface.

FIG. 7 provides a flow chart for a process 300A, which is an example of a process in which silylation 103 takes place in the same unit that a functional coating 401 is formed and protects a surface 404 of the functional coating 401 as the wafer 400 is transported or stored between processing units. Process 300A begins with actions taking place in a CVD module 310. Within the CVD module 310, a functional coating 401 is formed over the wafer surface 402. Hydrolysis 101 then takes place, if necessary, after which the surface 404 of the functional coating 401 is modified by silylation 103, which is also carried out in the CVD module 310. The wafer 400 is then transported to a cleaning module 320 where wet clean 301 takes place. In process 300A, silylation 103 can protect the surface 404 from hydrolysis during wet cleaning 301.

Process 300A continues with processing in a lithography module 210 and an etch module 220. Processing in these modules can be the same as described in relation to the process 200A. In this example, an additional action of forming an antireflective coating (not illustrated in the Figures) takes place prior to forming the photoresist 403. Silylation 103 can facilitate wetting of the surface 404 by a non-polar liquid and thereby forming a uniform antireflective coating over the surface 404.

FIG. 8 provides a flow chart for a process 300B, which is an example of a process in which silylation 103 takes place in a separate unit from the one in which functional coating 401 is formed. Process 300B is similar to process 300A except that silylation 103 takes place in cleaning module 320 following wet clean 301. If wet clean 301 leaves the surface 404 hydrolyzed, than an additional process of hydrolysis 101 is unnecessary. In process 300B, silylation 103 can protect the surface 204 from hydrolysis and defect formation during transport and storage in the ambient plant environment between cleaning module 320 and lithography module 210.

Within the ambient environment of a integrated circuit device manufacturing facility, environmental parameters such as humidity are uncontrolled or are controlled to only a limited extent. As a result, relatively high humidity, such a humidity in excess of 50% saturation, will routinely occur.

A wafer as the term is used herein is a semiconductor substrate and the various coatings and structures that are formed over that substrate. A semiconductor substrate can be, for example, silicon, silicon on insulator (SOI), Ge, SiC, GaAs, GaAlAs, InP, GaN SiGe. The surface of a wafer can be a surface of a coating on the substrate. The surface affected by silylation is generally an outer surface.

The present disclosure provides an integrated circuit device fabrication plant in which there are wafers having silyl ether groups are attached to their surfaces. The silyl ether groups are of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom.

The present disclosure provides a method of manufacturing integrated circuits in which hydroxyl moieties are formed on a surface over a semiconductor substrate. The surfaces are silylized to replace the hydroxyl groups with silyl ether groups, the silyl ether groups being of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom.

The present disclosure provides a method of manufacturing an integrated circuit device that includes processing a wafer in an integrated circuit device manufacturing facility and silylizing a surface of the wafer so that hydroxyl groups attached to the surface are replaced by silyl ether groups, the silyl ether groups being of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom. The wafer is then further processed within the integrated circuit manufacturing facility.

The components and features of the present disclosure have been shown and/or described in terms of certain embodiments and examples. While a particular component or feature, or a broad or narrow formulation of that component or feature, may have been described in relation to only one embodiment or one example, all components and features in either their broad or narrow formulations may be combined with other components or features to the extent such combinations would be recognized as logical by one of ordinary skill in the art. 

The claims are:
 1. A workpiece, comprising: a semiconductor wafer having surfaces; and a coating of silyl ether groups on the wafer surfaces, the silyl ether groups being of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom.
 2. The workpiece of claim 1, wherein the coating makes the surfaces hydrophobic.
 3. The workpiece of claim 1, wherein R₁, R₂, and R₃ are each selected from the group consisting of alkyl, vinyl, aryl, allyl, and alkynyl groups.
 4. The workpiece of claim 1, wherein the coated wafers are exposed to an ambient environment of the plant.
 5. A method of manufacturing integrated circuits, comprising: forming hydroxyl moieties or groups on a surface over a semiconductor substrate; and silylizing the surface to replace the hydroxyl moieties or groups with silyl ether groups, the silyl ether groups being of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom.
 6. The method of claim 5, further comprising: forming a coating over the semiconductor substrate within a processing unit having a controlled atmosphere; wherein the surface is a surface of the coating; and wherein the surface is silylized prior to removing the semiconductor substrate from the atmosphere of the processing unit.
 7. The method of claim 5, further comprising: cleaning the surface within a processing unit having the controlled atmosphere; wherein the surface is silylized after the cleaning but before removing the semiconductor substrate from the atmosphere of the processing unit.
 8. The method of claim 5, further comprising: forming a coating over the semiconductor substrate within a processing unit having a controlled atmosphere; wherein the surface is a surface of the coating; and wherein the coating is lithographically patterned and becomes incorporated into functional integrated circuit devices.
 9. The method of claim 5, wherein R₁, R₂, and R₃ are each selected from the group consisting of alkyl, vinyl, aryl, allyl, and alkynyl groups.
 10. The method of claim 5, wherein silylizing the surface comprises treating the surface with a silylating agent of the form YSiR₁R₂R₃, wherein Y is selected from the group consisting of halogens, halogen-containing compounds, amines, and amides.
 11. The method of claim 5, further comprising: forming a coating over the semiconductor substrate; forming the hydroxyl moieties on a surface of the coating; after silylizing the surface, forming a photoresist over the surface; selectively exposing the photoresist; and developing the photoresist.
 12. The method of claim 11, further comprising, after silylizing the surface but before forming the photoresist over the surface, curing the coating by baking.
 13. The method of claim 5, further comprising: depositing a coating over the semiconductor substrate; forming the hydroxyl moieties on a surface of the coating; after silylizing the surface, cleaning the surface in a wet cleaning process; and after cleaning, lithographically patterning the coating.
 14. The method of claim 13, wherein lithographically patterning the coating comprises: forming an antireflective coating directly over the silylized surface; and forming a photoresist over the antireflective coating.
 15. The method of claim 5, wherein forming the hydroxyl moieties comprises treating the surface with a solution comprising hydrofluoric acid.
 16. The method of claim 5, wherein forming the hydroxyl moieties comprises treating the surface with de-ionized or distilled water.
 17. A method of manufacturing an integrated circuit device, comprising: processing a wafer in an integrated circuit device manufacturing facility; silylizing a surface of the wafer whereby hydroxyl groups attached to the surface are replaced by silyl ether groups, the silyl ether groups being of the form: —OSiR₁R₂R₃, where R₁, R₂, and R₃ are each hydrocarbyl groups comprising at least one carbon atom; and further processing the wafer within the integrated circuit manufacturing facility after silylizing the wafer surface.
 18. The method of claim 17, wherein after silylizing but before further processing, the wafer is exposed to the ambient environment of the manufacturing facility.
 19. The method of claim 17, wherein the surface is that of a coating on the wafer and the surface is silylized within the processing unit in which the coating is formed.
 20. The method of claim 17, further comprising forming a coating over the silylized surface by applying to the surface a non-polar solution containing a precursor of the coating. 